Ontario Premier Doug Ford and Quebec Premier Francois Legault are urging both sides in the strike by 361 St. Lawrence Seaway workers to reach a deal right away.
They say they cannot have a repeat of the B.C. port workers strike back in July, and warn the seaway's shutdown could cause significant harm to the region's economy.
The strike has shut down the entire Welland Canal in Niagara, leaving ships stranded.
Ford and Legault say they are pleased the two sides are returning to the negotiating table along with federal mediators tomorrow, but want Ottawa to step in if there's no quick deal to end the strike.